1. Field of the Invention
The present invention relates to a receptor protein for a human B cell stimulatory factor-2 (hereinafter abbreviated as BSF2 receptor), a DNA sequence coding for the BSF2 receptor, and a process for the production of the BSF2 receptor using genetic engineering techniques.
2. Description of the Related Art
The B-cell stimulatory factor-2 (BSF2) is believed to be a factor which differentiates B-cells to antibody-producing cells. Recently, a cDNA coding for BSF2 was isolated, and on the basis of information relating to the DNA sequence and information relating to the partial amino acid sequence of the purified BSF2, the BSF2 was defined as a protein comprising 184 amino acid residues accompanied by a signal peptide consisting of 28 amino acid residues (T. Hirano, K. Yoshida and H. Harada et al, Nature, 324 73-76, 1986).
According to recent findings, the BSF2 is believed to induce B cells to produce antibodies; to stimulate the growth of hybridoma, plasmacytoma, myeloma and the like, to induce the expression of HLA class I antigens; to induce acute phase proteins on hepatocyte; and induce neuraxons (T. Kishimoto and T. Hirano, Ann. Rev. Immunol. 6. 485, 1985). As seen from the above, the BSF2 has various important physiological activities, and is extensively related to cell growth (Hirano et al, Summary of the 17th conference of Japan Immunology Association, pp 91,1987).
On the other hand, Hirano et al., Proc. Natl. Acad. Sci. U.S.A., Vol 84, pp 228, 1987, reported the possibility that an abnormal production of BSF2 is an etiology of an immune disorder in such diseases as cardiac mixoma, cervical cancer, myeloma, chronic articular rheumatism, Castleman's syndrome, and the like. Accordingly, an inhibitor of the BSF2 would be promising as a diagnostic, prophylactic or therapeutic agent for the above-mentioned diseases.
T. Taga et al., J. Exp. Med. 196, pp 967, 1987, analyzed a BSF2 receptor which is found on a cell membrane and specifically linked to the BSF2, and reported the number there on a cell and the binding constant with BSF2. The BSF2 receptor released from cell surface is promising as diagnostic, prophylactic and therapeutic agents and the like, and therefore, there is great interest in the progress of research into the BSF2 receptor.
To enable further progress in the research into the BSF2 receptor and the development of diagnostic, prophylactic and therapeutic agents, the availability of a large amount of purified BSF2 receptor is essential, although the receptor can be produced in vivo in only a very small amount.
For the production of proteins, such as the BSF2 receptor, present in a very small amount in an organism, a genetic engineering technique also known as genetic manipulation is used. In this technique, a DNA sequence coding for a desired protein is cloned, the cloned DNA sequence is operatively linked with control DNA sequences such as a promoter, and the DNA sequence is inserted into a vector to construct an expression vector, which is then used to transform host cells. The transformant is cultured to produce the desired protein. To use such a genetic engineering procedure to produce a target protein, it is necessary to obtain a DNA sequence coding for the target protein. However, the gene coding for the BSF2 receptor has not yet been cloned.